Recently, downsizing and weight saving have been carried out with respect to electronic devices such as portable information terminals In response thereto, there have been demands for downsizing, weight saving, and high density packaging with respect to semiconductor integrated circuits for use in such electronic devices.
Semiconductor integrated circuits and the like (hereinafter semiconductor devices) are manufactured through various processing steps. The processing steps include many processes, such as cleaning, etching, and plating, in which chemical solutions are used.
Taking formation of a bump electrode by plating (metal plating process) as an example, the following outlines a process in which a chemical solution is used.
Note that the bump electrode is an electrode for mounting (installing) a semiconductor device on an actual substrate of an electronic device. The mounting of the semiconductor device by using the bump electrode is widely employed as a useful method for attaining the downsizing and high density packaging of the semiconductor device.
In this mounting method, first, by using a plating technique, a bump electrode made of gold (Au) or the like is formed at a predetermined position on a front surface of a semiconductor device. Then, by using the bump electrode, the semiconductor device is directly mounted on a substrate to be mounted.
In the formation process of the bump electrode, first, a photoresist is applied to a front surface of a semiconductor substrate on which the semiconductor device has been mounted. Then, the photoresist film of a predetermined portion at which the bump is removed, so that a base metal film, which has been laminated in advance, is exposed.
After that, the semiconductor substrate is soaked in a plating solution. The bump electrode is formed by depositing plating metal (e.g. gold (Au)) on the base metal film that has been exposed after the photoresist film was removed.
Incidentally, the plating process causes that the plating metal may be deposited also on portions, other than the predetermined portion on the semiconductor substrate, i.e., on deviant portions such as a back surface of the substrate or a supporting mechanism of the substrate.
The plating metal deposited on such deviant portions is partially exfoliated from the substrate, floats or precipitates as a foreign substance in the plating solution, and moves in a plating apparatus in accordance with a flow of the plating solution. The plating solution is contaminated with plating metal particles, air bubbles, dust in the air, and the like, in some cases.
Thus, in the plating solution, there are floating and precipitated various foreign substances that have different sizes and specific gravities. These foreign substances circulate in the plating apparatus in accordance with the fluxion of the plating solution.
If these foreign substances are attached to the front surface of the substrate while the plating process is carried out, various problems are caused, such as plating error at those portions where the foreign substances are attached, or a short circuit between bump electrodes.
Therefore, in carrying out the plating process, it is necessary to pay attention to removal of the foreign substances contaminating the plating solution, as much as or more than it is necessary to pay attention to evenness of the plating.
In this regard, conventionally, a partition plate is provided in a plating tank so as to remove the foreign substances.
FIG. 6 is an explanatory diagram illustrating an arrangement of a conventional plating apparatus 101. As shown in the FIG. 6, the plating apparatus 101 includes a plating tank 111, a plating solution supply nozzle 112, a plating solution discharge nozzle 113, a circulation pump 114, a partition plate 116, a plating solution 117, a filter 119, and a gap 120 (a gap between the partition plate and a bottom surface of the plating tank).
The partition plate 116 partitions the plating tank 111 into a region A, into which the plating solution 117 flows, and a region C, in which the plating is carried out.
An upper end of the partition plate 116 is higher than a liquid surface of the plating solution (chemical solution) 117. Between a lower end of the partition plate 116 and the bottom surface of the plating tank 111, the gap 120, which is predetermined, is provided.
In the plating apparatus 101 having the arrangement above, the plating solution 117 is pressurized by the circulation pump 114. Then, the plating solution 117 passes through the filter 119, and flows via the plating solution supply nozzle 112 into the region A of the plating tank 111. After that, the plating solution 117 that have flown into the region A passes through the gap 120, and flows into the region C of the plating tank 111.
The plating solution 117 in the region C is discharged from the plating solution discharge nozzle 113. Then, the plating solution 117 is again pressurized by the circulation pump 114, so that the plating solution 117 circulates in the plating tank 111.
In the plating apparatus 101, light foreign substances (foreign substances that are smaller in specific gravity than the plating solution 17, and/or air bubbles in the plating solution 117) that have flown with the plating solution 117 into the region A rise to the liquid surface of the plating solution 117.
As described above, the upper end of the partition plate 116, which separates the region A and the region C, is higher than the liquid surface of the plating solution 117. Therefore, the foreign substances that have risen are dammed by the partition plate 116, and remain in the region A, without flowing into the region C.
Thus, the plating apparatus 101 is provided with the partition plate 116 so as to remove the light foreign substances from circulation of the plating solution 117.
However, in the plating apparatus 101 shown in FIG. 6, there is a possibility that some of the light foreign substances flow into the region C through the gap 120, which is at a lower portion of the partition plate 116, in response to the fluxion of the plating solution 117.
In contrast, foreign substances that are greater in specific gravity than the plating solution 117 (heavy foreign substances) sink to the bottom surface of the region A. Therefore the heavy foreign substances easily flow into the region C in accordance with the flow of the plating solution 117.
Most of the heavy foreign substances that have flown into the region C are discharged out of the plating tank 111 via the plating solution discharge nozzle 113, but again flow into the plating tank 111, together with the plating solution 117 circulated by the circulation pump 114. This causes that the foreign substances in the plating tank 111 (region C) increase with time.
To overcome this drawback, the plating apparatus 101 includes, as shown in FIG. 6, the filter 119 provided so as to follow the plating solution discharge nozzle 113 and the circulation pump 114, so that the foreign substances in the platting solution 117 are removed.
However, in the plating apparatus 101 shown in FIG. 6, in order to effectively remove the foreign substances in the plating solution 117, it is necessary to use (allocate as appropriate) a plurality of filters 119 in accordance with sizes and types of the foreign substances.
With time, the filter 119 becomes clogged with the foreign substances. Therefore, periodical maintenance such as replacement of the filter 119 is required. This is a heavy burden in terms of time and labor necessary for performing the maintenance, such as purchase and replacement of the filter 119.
In the foregoing explanation, problems (issues) on emergence and removal of the foreign substances are discussed, taking the plating apparatus (plating tank) as an example.
Note that the emergence of the foreign substances and necessity to remove the foreign substances are no less significant than in the plating apparatus in other liquid flow processing apparatuses (apparatuses that involve inflow and outflow of a liquid (liquid flow process); e.g. a cleaning apparatus using a chemical solution) used in steps of manufacturing semiconductor devices or other devices (e.g. liquid crystal panels).